1. Technical Field
The present invention relates generally to a printer which prints an image on printing paper via a printing head. More particularly, the invention relates to a thermal printer which provides for easy replacement of rolls of printing paper.
2. Background Art
Japanese Patent First Publication (tokkaisho) No. 63-1571, corresponding to U.S. Pat. No. 4,848,945, commonly owned with this application discloses a thermal printer in which a thermal head prints an image on thermosensitive paper drawn from a roll thereof. This printer includes a paper housing provided within a sub-chassis for storing the roll of paper. This sub-chassis is laterally slidable outward from the printer main chassis so as to expose the paper housing for easy loading of the roll of paper into it. This sliding movement is performed by a sliding system which operates in cooperation with ahead shifter for shifting up and down the thermal head against a platen roller rotatably supported by the main chassis. Withdrawing the sub-chassis causes the head shifter to separate the thermal head from the platen roller, while pushing back the sub-chassis into the printer causes the thermal head to be urged against the platen roller with the printing paper therebetween.
Such a conventional printer employs a so-called linear skating system wherein the sub-chassis moves parallel to the main chassis. This linear skating system essentially requires a sliding mechanism, such as long sliding rails, to expose the paper housing provided within the sub-chassis. The sliding rails consequently increase the size of the printer.
The coordinated movement of a head shifting system with the withdrawing movement tends to complicate the linkage between the sliding mechanism and the head shifter. There are therefore problems in assembly and reliability, as well as increased production costs.
Additionally, once a roll of paper is loaded into the paper housing of the sub-chassis, the thermal head is kept pressed to the platen roller, causing undesired pressure on the platen roller.
Further, in the conventional printer, a shaft or similar mechanism provides support for the platen roller, such that movement thereof relative to the sub-chassis is achieved, and positioning errors between the platen roller and the thermal head and prevented. Due to variations in the assembly accuracy of the platen roller relative to the sub-chassis, accurate positioning between the platen roller and the thermal head is difficult.